How Leukemia is Diagnosed

Technician holding blood sample
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Making an accurate diagnosis of leukemia is important in choosing the best treatment options. Testing often begins with a complete blood count and peripheral smear. A bone marrow aspiration and biopsy are done with most types of leukemia. Tests are then done to look for surface markers on the cells (flow cytometry) as well as genetic changes (either chromosomal or gene changes) with cytogenetic testing.

With some leukemias, a lumbar puncture (spinal tap), or lymph node biopsy may be done as well. Imaging studies such as x-ray, CT, MRI, and PET scans, are not usually an important part of the diagnosis as they are for other types of cancers. Staging also differs from solid tumors, and can include factors such as symptoms, the subtype of leukemia, the number of abnormal cells in the blood or bone marrow, and more.

When talking about diagnosis, it's important to note that leukemia is not one disease or even four diseases, but rather there are many different variations of the disease. Two leukemias that appear identical under the microscope may behave very differently, and some of the tests below may help to distinguish some of the differences.

The history and physical are the starting point in the diagnosis of leukemia and what often prompts doctors to order further studies, but cannot make the diagnosis alone.

A careful history will be done to ask about the symptoms of leukemia, as well as to look for any risk factors for leukemia. A physical examination may reveal signs that suggest a condition such as leukemia may be present, such as swelling of lymph nodes, the spleen, or liver, pale skin or lightheadedness (signs of anemia), bruising or bleeding (signs of a low platelet count), or recurrent infections.

 

Blood Tests

Simple blood tests are the first step in diagnosing leukemia. Both a complete blood count and peripheral smear can give important clues as to the diagnosis and type of leukemia, and guide further evaluation.

Complete Blood Cell Count

complete blood count (CBC) measures the numbers of each of the major types of blood cells made by the bone marrow: the white blood cells, red blood cells, and platelets. The CBC can also give numbers that relay important numbers about these types of blood cells, such as whether the red blood cells are large or small. While there is often an increase in white blood cells with leukemia, with acute leukemia there is sometimes a decrease in all of the types of blood cells including white blood cells, a condition referred to as pancytopenia.

Peripheral Blood Smear and Differential

A peripheral smear is a very important test when considering the diagnosis of leukemia. In a peripheral smear, a sample of blood is spread on a microscope slide and dye is added. The smear is then evaluated under the microscope. A CBC can determine if a white blood cell count is low or high, but doesn't give enough information about the type of white blood cells that are increased or decreased.

It also doesn't tell a doctor whether there are immature white blood cells called "blasts" in the peripheral blood; cells that are normally only found in significant numbers in the bone marrow.

Typical findings (these can vary) on a CBC and blood smear for the four main types of leukemia include:

Disease

CBC Results

Blood Smear Results

Acute Myelogenous Leukemia (AML)

•Lower than normal amounts of red cells and platelets

•Too many immature white cells, and sometimes the presence of Auer rods

Acute Lymphocytic Leukemia (ALL)

•Lower than normal amounts of red cells and platelets

•Too many immature white cells

Chronic Myelogenous Leukemia (CML)

•Red blood cell count may be high and platelet count may be high or low
•White blood cell count may be very high

•May show some immature white cells
•Mainly high numbers of fully mature white blood cells

Chronic Lymphocytic Leukemia (CLL)

•Red cells and platelets may or may not be decreased
•White blood cell count may be very high (over 20,000 cells/mm3 and sometimes over 100,000 cells/mm3)

•Little or no immature white cells
•Possibly fragments of red cells

 

Some of the tests discussed below under bone marrow biopsy (such as cytochemistry), may also be done on peripheral blood.

Bone Marrow Aspiration and Biopsy

With most types of leukemia, blood tests are not enough to conclusively diagnosis the disease, and a  bone marrow aspiration and biopsy are done. (With CLL, the diagnosis can sometimes be made based on the blood tests above, but a bone marrow can still be helpful in determining how advanced the cancer is.) The bone marrow is the source of the cancer cells in leukemia, and is the source of all of the blood cells found in the peripheral blood. 

With a bone marrow aspiration, a long, thin needle is inserted into the bone marrow in the hip (or sometimes the breastbone) after numbing the skin locally with lidocaine. After a sample of the bone marrow is aspirated, a biopsy sample is also taken.

In normal bone marrow, between 1 percent and 5 percent of cells are "blast cells" or the immature white blood cells that mature into the blood cells normally found in the blood. A diagnosis of ALL can be made if 20 percent to 30 percent of the cells are blasts (lymphoblasts). With AML, a diagnosis can be made if there are less than 20 percent blasts (myeloblasts) if a specific chromosome change (see below) is also found.

In addition to looking at the number of different cells present in the bone marrow, doctors also look at the pattern of the cells. For example, with CLL, the prognosis of the disease is better if the cancer cells are found diffusely scattered around the bone marrow than if they are found in groups (nodular or interstitial pattern). The ration of leukemia cells to healthy blood-forming cells can be significant in the diagnostic process.

Cytochemistry

Cytochemistry looks at how the cells in the bone marrow take up certain stains, and can be helpful in distinguishing ALL from AML. Tests can include both flow cytometry and immunohistochemistry.

Flow Cytometry and Immunohistochemistry (Immunophenotyping)

In flow cytometry, the bone marrow cells (or peripheral blood cells) are treated with antibodies to look for the presence of certain proteins found on the surface of the cells (the antibodies stick to these proteins). Immunohistochemistry is similar, but instead of using a laser that causes the cells to give off light, it looks for a color change that can be seen under the microscope.

This process of looking for unique proteins on the surface of cells is referred to as immunophenotyping. In genetics, genotype refers to the characteristics of a gene, whereas phenotype describes physical characteristics (such as blue eyes). Different types of leukemia differ in these "phenotypes."

With acute leukemias (both ALL and AML), these studies can be helpful in determining the subtype of the disease, and with ALL, can determine if the leukemia involves T cells or B cells. In addition, these tests can be very helpful in confirming a diagnosis of CLL (by looking for proteins called ZAP-70 and CD38).

Flow cytometry can also be used to determine the amount of DNA in leukemia cells, which can be helpful in planning treatment. ALL cells that have more DNA than an average cell tend to respond better to chemotherapy.

Chromosome and Gene Studies

Leukemia cells very often have changes in the chromosomes or genes found in the DNA of each cell. Each of our cells normally has 46 chromosomes, 23 from each parent. Each of these chromosomes contains many genes. Some studies look primarily at chromosomal changes, whereas others look for changes in specific genes.

Cytogenetics

Cytogenetics involves looking at the chromosomes of cancer cells under the microscope and looking for abnormalities. Due to the method by which this is done—the cancer cells need time to be grown in the lab after being retrieved—the results of these studies are often not available for 2 weeks to 3 weeks after a bone marrow biopsy is done. 

Chromosomal changes that may be seen in the leukemia cells include:

  • Deletions: In a deletion, part of a chromosome is missing or "deleted."
  • Translocations: In a translocation, pieces of two chromosomes are exchanged. This may be a complete exchange, in which pieces of DNA are simply swapped between two chromosomes, or instead may be a partial translocation. For example, DNA may be swapped between chromosomes 9 and 22. Chromosome translocations are very common in leukemia, occurring in up to 50 percent of these cancers.
  • Inversion: An inversion involves part of a chromosome remaining present, but turned around (as if a piece is removed and replaced but backward).
  • Addition or Duplication: In an addition or duplication, extra copies of all or part of a chromosome are found.
  • Trisomy: In trisomy, there are 3 copies of one of the chromosomes rather than two.

In addition to further defining the type of leukemia, cytogenetics can help with planning treatment. For example, in ALL, leukemia cells that have more than 50 chromosomes respond better to treatment

FISH (Fluorescent In Situ Hybridization)

Fluorescent in situ hybridization or FISH is a procedure that uses special dyes to look for changes in chromosomes that can't be detected under the microscope, or changes in specific genes.

With chronic myelogenous leukemia (CML), this test can look for pieces of the BCR/ ABL1 fusion gene  (Philadelphia chromosome). Roughly 95 percent of people with CML will have the Philadelphia chromosome (shortened chromosome 22), but the other 5 percent will still have the abnormal BCR/ABL1 fusion gene on further testing. (The Philadelphia chromosome is also an important finding with ALL.)

With CLL, cytogenetics (looking at whole chromosomes) is less helpful, and FISH and PCR are more important in finding genetic changes. There are many genetic abnormalities that may be seen in these studies, including deletions in the long arm of chromosome 13 (in half of the people with the disease), an extra copy of chromosome 12 (trisomy 12), deletions in the 17th and 11th chromosome, and specific mutations in genes such as NOTCH1, SF3B1, and more.

PCR (Polymerase Chain Reaction)

Like FISH, polymerase chain reaction, or PCR can find changes in chromosomes and genes that can't be seen under a microscope (through cytogenetics). PCR is also helpful in finding changes that are present in just a few, but not all, of the cancer cells.

PCR is very sensitive in finding the BCR/ABL gene, even when other signs of CML aren't found on chromosome testing.

Lymph Node Biopsy

Lymph node biopsies, in which part or all of a lymph node are removed, are done infrequently with leukemia. A lymph node biopsy may be done with CLL if large lymph nodes are present, or if it's thought that CLL may have transformed into a lymphoma.

Lumbar Puncture (Spinal Tap)

With some types of leukemia, a spinal tap (lumbar puncture) may be done to look for the presence of leukemia cells that have spread into the fluid surrounding the brain and spinal cord. It may be done for those with ALL, as well as people with AML who have any neurological symptoms suggesting this spread.

In a lumbar puncture, a person lies on a table on their side with knees up and head down. After cleaning and numbing the area, a doctor inserts a long thin needle into the lower back, between the vertebrae, and into the space surrounding the spinal cord. Fluid is then withdrawn and sent to a pathologist to be analyzed.

Imaging

Imaging tests are not usually used as a diagnostic method for leukemia, as blood-related cancers like leukemia don't often form tumors. It may be helpful, however, in staging some leukemias, such as CLL.

X-Rays

X-rays, such as a chest x-ray or bone x-ray are not used to diagnose leukemia, but may give the first signs that something is wrong. An x-ray may show enlargement of lymph nodes, or thinning of bones (osteopenia).

CT

A CT scan uses a series of x-rays to create a 3-dimensional picture of the inside of the body. CT may be helpful in looking at nodes in the chest or other regions of the body, as well as noting enlargement of the spleen or liver.

MRI

An MRI used magnets to create a picture of the inside of the body, and does not involve radiation. It may be helpful in leukemias that involve the brain or spinal cord.

PET/CT or PET/MRI

In a PET scan, radioactive glucose is injected into the body, where it is taken up by cells that are more metabolically active (such as cancer cells). PET is more helpful with solid tumors than with leukemia, but may be helpful with some chronic leukemias, especially when there is concern about transformation into a lymphoma.

Differential Diagnosis

There are some diseases that, at least with initial testing, may resemble leukemia. Some of these include:

  • Certain viral infections: For example, the Epstein Barr virus (the cause of infectious mononucleosis), cytomegalovirus, and HIV may cause an elevated number of atypical lymphocytes on blood tests.
  • Myelodysplastic syndromes: These are diseases of the bone marrow that have a predilection for developing into AML and are sometimes referred to as "preleukemia."
  • Myeloproliferative disorders: Conditions such as polycythemia vera, essential thrombocytosis, primary myelofibrosis, and more may resemble leukemia prior to the in-depth testing methods above.
  • Aplastic anemia: A condition in which the bone marrow stops making all of the types of blood cells.

Staging

Staging refers to the system used by doctors to categorize a cancer. Determining the stage of a cancer, in general, can help doctors select the most appropriate treatment as well as estimate the prognosis of the disease.

Leukemias are staged differently than solid tumors, and differs between the different types of leukemia. Since many leukemias do not form solid masses, staging (with the exception of CLL) is very different from that of solid tumors such as breast cancer or lung cancer.

A number of studies may be taken into consideration in assigning a stage, such as the number of immature white blood cells found in the blood or bone marrow, tumor markers, chromosome studies, and more.

When looking at staging, it's again important to note that leukemia is a wide range of diseases. Two people with the same kind of leukemia and the same stage may have very different responses to therapy, and different prognoses.

Chronic  Lymphocytic Leukemia

For chronic lymphocytic leukemia or CLL, there are a number of different staging systems that may be used. Most common is the Rai system. In this system, these leukemias are given a stage between stage 0 and stage 4 based on the presence of several findings:

  • High numbers of lymphocytes
  • Enlarged lymph nodes
  • An enlarged liver and/or spleen
  • Anemia
  • Low levels of platelets

Based on these stages, the cancers are then separated into low, intermediate, and high-risk categories.

In contrast, the Binet system used in Europe, separates these leukemias into only three stages:

  • Stage A: Less than 3 lymph nodes
  • Stage B: Greater than 3 affected lymph nodes
  • Stage C: Any number of lymph nodes, but combined with either anemia or a low level of platelets.

Acute Lymphocytic Leukemia

For acute lymphocytic leukemia or ALL, staging is different, as the disease does not form tumor masses that extend incrementally from an original tumor. ALL will likely spread to other organs even before it is detected, so rather than using traditional staging methods, physicians often factor in the subtype of ALL and the person's age. This usually involves cytogenetic tests, flow cytometry and other lab tests to identify the subtype of ALL.

Rather than using stages (those used in the past are largely obsolete), ALL is more often defined by the "phases" of the disease. These include:

  • Untreated ALL
  • ALL in remission
  • Minimal residual disease
  • Refractory ALL
  • Relapsed (recurrent) ALL

Acute Myelogenous Leukemia

Similar to ALL, with acute myelogenous leukemia or AML the disease is usually not detected until it has spread to other organs, and so traditional cancer staging is not applicable. Staging is determined by characteristics such as the subtype of the leukemia, a person's age, and more.

An older staging system, the French-American-British (FAB) classification, classified AML into eight subtypes, M0 through M7, based on the appearance of the cells under the microscope. The World Health Organization (WHO) developed a different system for AML staging with the hope of more closely predicting the prognosis of the disease. In this system, these leukemias are separated out by characteristics such as chromosomal abnormalities in the cells (some chromosome changes are associated with a better than average prognosis and some are associated with poorer outcomes), whether the cancer arose after previous chemotherapy or radiation ( secondary cancers), those related to Down syndrome, and more.

Chronic Myelogenous Leukemia

For chronic myeloid leukemia or CML, staging is determined based on the number of immature blood cells in the blood or bone marrow, and the symptoms that are present:

  • Chronic phase: In this earliest stage, there are less than 10 percent blasts in the blood or bone marrow and symptoms are either mild or absent. People in the chronic phase of CML usually respond well to treatment.
  • Accelerated phase: In the next phase, 10 percent to 20 percent of the cells in the blood or bone marrow are blasts. Symptoms become more pronounced, particularly fever and weight loss. Testing may reveal new chromosomal changes in addition to the Philadelphia chromosome. People in the accelerated phase of CML may not respond to treatment.
  • Blast phase (aggressive phase): In the blast phase of CML, more than 20 percent of the cells in the blood or bone marrow are blasts, and blast cells may also spread to areas of the body outside of the bone marrow. During this phase, symptoms include fatigue, fever, and an enlarged spleen (blast crisis).

 

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